Many thanks for looking into this, MK14!
The ESP32s do look tempting indeed -- seems like they have well-developed touch sensing, are cost-effective, and still reasonably available. My only reason not to use them in my current project is the need for many pins, as mentioned above.
I have given up on Atmel as well as Microtech (PICs). With both of them, it seems that capacitivce touch was a thing before 2010 or so, and then they stopped maintaining it. Datasheets mention the hardware capability, but their QTouch or mTouch tools can't be trusted to support it. The ATmega2560 should be supported if you don't use the configuration tool, but then their official library example code required an outdated version of the ASF framework which is nowhere to be found... While I have used the ATtiny and ATMega family a lot, I can't be bothered with documentation and software archeology... Microchip's documentation seems poorer than Atmels in general (even back when it was up to date).
Renesas looks like a strong contender -- well-developed touch functionality, decent and up-to-date documentation. But their MCUs seem geared towards professional customers; I could not find many project examples on the 'net, and many processor types are apparently not stocked by Mouser even in normal times. And I did not feel like learning yet another new IDE...
For the moment I have settled on an STM32 -- after finding one which is actually available. STM has not the greatest touch support: No proper mutual capacitance sensing; keyboard matrices are possible, but they measure the capacitance of the row and column lines independently (capacitance against the environment). So one probably does not get the robustness improvement, and they can't do multi-touch. But I have used STM32 processors before and know my way around their IDE; and their documentation seems current and quite decent.
If and when my "Enigma touch" actually becomes reality, I'll post an update here. I have started to play with component layout and front panel design, but getting the touch hardware and software to work will defnínitely take a while. Maybe a project for the Christmas break?
Thanks for the nice, detailed, clear and very quick response.
That sounds very sensible. The STM32's, are just (in some cases), suffering from the same component shortages, as other MCUs (give or take a bit).
We are in strange times (component shortage wise). Despite, having an involvement with electronics, for rather a long time. I've never seen it like this. It reminds me of (reports), about World War 2, where all sorts of items were (understandably), in short supply or unavailable.
You hadn't seemed to post in the thread for a while, so I was somewhat confused as to what had happened.
I was always somewhat fascinated by touch panels. With the early/original CMOS logic devices (4000 series), you just needed to forget to connect an input, to accidentally create a touch switch effect.
The complication (my own issue), that I have with some of the modern MCUs. Is they can have data manuals/guides, which can total 15,000 pages (very, very approximate number indeed). Which (unlike the old days, when the MCU databook, was something you could physically obtain, and potentially read its 250..500+ or so (estimated) pages, over a quiet weekend, and then (feel like you) know almost everything there is about that MCU.
Also the 8 bit (original) MCUs, were so much easier to use, in days of old.
Things can get rather scary (data sheet/book) wise, these days. My mind still gets blown by the functionality, of the very high end MCUs these days. Even things like Ethernet, graphics, full cryptographic systems, etc, can be built in. Probably more functionality and computing power, than a typical standard PC, from perhaps 30 years ago (very approximately).
It seems to boil down to learning new skills, whereby you have to accept, reading the entire range of data books/sheets and app notes, on a particular (high end), MCU, is not especially practicable. So, limiting oneself, to searching or seeking out the relevant sections, is what seems to be best.
You seem just right as regards Renesas.
You do realize that Atmel doesn't exist anymore, since it merged into Microchip?
Yes, I know. But some of their chips, such as the Arduino ones, still seem quite popular, and have quite a lot of projects and information available, for them.